The polymerization of lactone monomers and the copolymerization of lactone monomers and epoxide monomers yield polymeric products useful in a wide variety of applications. For example, caprolactone polyols find utility in polyurethane coatings, adhesives, and thermoplastic urethane and castable polymers. Higher molecular weight lactone polymers serve as processing aids and modifiers for resins such as ABS and polycarbonate and as hot melt adhesives. Aliphatic polyesters such as polycaprolactone exhibit exceptionally high compatibility or miscibility with a variety of common polymeric resins.
Lactones have been successfully polymerized using several different types of catalysts including, for example, metalloporphyrin catalysts, bimetallic oxoalkoxides, mixed alkoxyalkyl compounds of zinc and tin, alkyllithium compounds, basic catalysts such as alkali metal hydroxides and Lewis acid catalysts such as boron trifluoride. A general discussion of lactone polymerization may be found in K. Ivin and T. Saegusa, Ring-Opening Polymerization, Vol. 1, Chapter 7, pp 461-521.
Some of the known lactone polymerization catalysts are known to have certain practical limitations. These limitations include: the occurrence of undesirable side reactions; the lack of complete control over molecular weight, molecular weight distribution, or end-group functionality; the need to use relatively large concentrations of catalyst. Thus, development of an improved catalytic process wherein these difficulties may be avoided would be highly desirable.